Breast cancer researchers have found three more genes linked to the most
common form of breast cancer, which they have alikened to "finding gold".

The genes could lead to new ways of diagnosing and treating hormonal breast cancer, also known as oestrogen receptor positive breast cancer, which is responsible for four out of five cases, or 36,000 a year in Britain.

In particular, they found one gene which appears to drive the growth of tumours.

The scientists, from the Breakthrough Breast Cancer Research Centre at The Institute of Cancer Research (ICR) in London, said the discovery could in the future help patients whose breast cancers do not respond to drugs like tamoxifen.

They located the genes - named C6ORF96, C6ORF97 and C6ORF211 - in a very well studied part of the human genome, next to the oestrogen receptor gene, which is the main driver of hormonal breast cancer.

Dr Anita Dunbier, lead author of the study, which is published in the journal PLoS Genetics, said: "This is a surprising discovery. We found these genes in a place we thought we knew a lot about - it is like finding gold in Trafalgar Square.

"We now have to look further at how these genes work, but the discovery could lead to possible new therapies that will benefit women with breast cancer in the future."

She added: "What we have found helps us understand more about this type of breast cancer and provides some potential avenues of therapy."

She explained that most drugs - such as aromatase inhibitors - targeted the oestrogen receptor itself.

However, they did not target genes that were associated with the receptor but separate from it - genes which she said could help tumours resist today's drugs.

"If we can target these genes, we can treat resistant tumours better," said Dr Dunbier.

She and her colleagues studied the DNA of 104 women with oestrogen receptor positive breast cancer, specifically looking for genes closely linked to the receptor itself.

The most exciting gene target for drugs is C6ORF211, which appears to drive tumour growth. Presence of C6ORF97 appears to indicate a patient will respond to tamoxifen, a drug which interferes with the activity of oestrogen. Researchers do not know exactly what C6ORF96 does.

Professor Mitch Dowsett, who leads the team at the Breakthrough Breast Cancer Research Centre, said: "This research is exciting because it shows that while the oestrogen receptor is the main driver of hormonal breast cancer, there are others next door to it that also appear to influence breast cancer behaviour.

"We now need to better understand how they work together and how we can utilise them to save lives of women with breast cancer."